Photo-electrochemical etching in KOH aqueous solutions was used to study defects in N-polar hetero-epitaxial GaN layers. Detailed cross-sectional transmission electron microscopic study of photo-electrochemically-etched material revealed that apart from dislocations, also inversion domains give rise to the formation of etch features. When the diameter of inversion domains remained in the tens of nanometer range, the defects were entirely resistant to the etching medium. However, inversion domains with diameters above the critical value (about 80nm) were preferentially etched in their centers, resulting in the formation of pronounced crater-like etch features. This indicated that photo-etching of GaN took place via the so-called electroless mechanism, with the critical role of holes for surface reactions and points at the recombinative property of inversion domain boundaries.

Complementary Study of Defects in GaN by Photo-Etching and TEM. J.L.Weyher, L.Macht, F.D.Tichelaar, H.W.Zandbergen, P.R.Hageman, P.K.Larsen: Materials Science and Engineering B, 2002, 91-92, 280-4